Traditional men's cummerbund

The broad, fabric waist sash that is used to jazz up men's formal wear, is a fashion statement that has its roots in the Persian kamarban (a long coloured sash that was wrapped around a tunic) and was popularised in the West via British Colonial India, when it was used as a lighter and more comfortable alternative to the waistcoat. Cummerbund sashes, usually made of silk,  often included convenient horizontal pleats that could store ticket stubs and other sundry items when a gentleman was out and about.

US Marine Corp evening dress uniforms.
Gucci is right into cummerbunds
Apart from being a feature of many military dress uniforms, the fashion spread further afield, to civilian populations in Europe and the US and is still standard male attire at many weddings, dinners and other formal events - although cummerbund dress purists decry the modern trend of wearing a matching bow tie and cummerbund, as traditionally the cummerbund was crimson or matched the trousers (usually black) and never the bow tie.

Very popular for formal wear in the 1930s, cummerbunds suited the high-waisted pants style of the era and were  worn with a black single breasted jacket, while the flamboyant and night club bands wore a striking white version.

1950s cummerbunds
A 1950s Dress Feature
In the 1950s and early 1960s , the pleated cummerbund also became popular as an accent on women and children's dresses, often colour coordinated or in striking, contrast multi-colours.

These were very well made, lined or double fabric and wrapped around the waist without puckering up or rolling into a skinny band as many of the modern elasticised 'pretend cummerbands' tend to do.

Cummerbunds are a style plus on the right dress as they can transform the look  and really emphasize a waistline, though I'd guess not so good for those us with a few spare rolls of fat spilling out over either side of the sash.